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Issue 17 | April 2015
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Dear Colleagues,
Welcome to our 17th edition of AstroPAH. This issues Picture of the Month features
an X-ray image of the supernova remnant N132D in the Large Magellanic Cloud. This
supernova remnant shows signs of PAH processing.
In Focus we have an interview with Dr. Melanie Schnell, who has just been awarded
an ERC starting grant to work, amongst other topics, on rotational spectroscopy of PAH
complexes.
In our abstracts section, you can find new studies on PANHs, PAH clusters, nanodiamonds, and dust as well as a look into unidentified emission features. Not included
in AstroPAH, but now available online, are the abstracts of the 69th International Symposium on Molecular Spectroscopy (June 16-20, 2014 at The University of Illinois at
Urbana-Champaign).
We would like to draw your attention to our meetings and announcements sections
featuring two interesting meetings next September – the symposium to honour Lou Allamandolas contributions to the molecular Universe in Annapolis (USA) and the International Symposium on Polynuclear Aromatic Hydrocarbons in Bordeaux (France) – and
the recent launched journal Molecular Astrophysics.
We thank you all for your contributions and please keep them coming. You can send
us your contributions anytime. For publication in May, see the deadlines below. Would
you like to see your picture as Picture of the Month, your project featured in our In Focus,
or distribute your latest paper or upcoming event amongst our community, we encourage
you to contact us (astropah@strw.leidenuniv.nl).
The Editorial Team
Next issue: 19 May 2015.
Submission deadline: 8 May 2015.
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AstroPAH - April 2015 | Issue 17
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Contents
AstroPAH Newsletter
EDITORIAL BOARD:
PAH Picture of the Month
Editorial
In Focus: Melanie Schnell
Recent Papers
Editor-in-Chief
Prof. Alexander Tielens
Leiden Observatory (The Netherlands)
Executive Editor
Dr. Isabel Aleman
Leiden Observatory (The Netherlands)
Editors
Dr. Alessandra Candian
Leiden Observatory (The Netherlands)
1
2
4
8
Meetings
12
Announcements
14
PAH Picture of the Month
Chandra X-ray Observatory view of the supernova remnant (SNR) N132D, in the Large
Magellanic Cloud. The colors in this image show emission due to low energy X-rays
(red, 0.3-0.5 keV), intermediate energy X-rays
(green, 0.5-0.75 keV) and high energy X-rays
(blue, 0.75-7 keV). N132D is one of the very
few SNRs showing clear evidence for large
PAH molecules being destroyed by the blast
wave shock (Tappe et al, 2012, ApJ, 754,
132).
Dr. Elisabetta Micelotta
Institut d’Astrophysique Spatiale
CNRS/Universite´ Paris-Sud (France)
Dr. Annemieke Petrignani
Leiden Observatory and
Radboud University Nijmegen
(The Netherlands)
Dr. Ella Sciamma-O’Brien
NASA Ames Research Center (USA)
Credits: NASA/CXC/NCSU/K. J. Borkowski
et al.
CONTACT
CLICK HERE TO
astropah@strw.leidenuniv.nl
SUBSCRIBE TO AstroPAH
CONTRIBUTE TO AstroPAH!
http://astropah-news.strw.leidenuniv.nl
Design by Isabel Aleman
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Interview with Melanie Schnell
Tell us about yourself.
Melanie: ”I am a physical chemist by training with a molecular
physics and theoretical chemistry background as well. With my
PhD research in the group of Jens-Uwe Grabow at the University of Hannover, I started to work in the field of high-resolution
rotational spectroscopy. My main research focus was on investigating highly flexible molecules, but I soon also got in contact
with my first PAH. . .
After my PhD I changed the field a bit to develop new methods
to guide, decelerate and trap neutral, polar molecules in the gas
phase using electric fields via their Stark effect – a very fascinating area of research.
Since 2011, I am back in molecular spectroscopy. I am currently a Max Planck research group leader at the Max Planck
Institute for the Structure and Dynamics of Matter in Hamburg.
In the group, we have a strong focus on investigating the structure, dynamics, and chirality of
molecules and molecular complexes in the gas phase using broadband rotational spectroscopy
employing the new chirp approach. Among others, we are interested in molecules of biological
relevance. We also have a strong focus on molecular complexes, to learn about the interplay
between the different molecular interaction forces.
As you all know, rotational spectroscopy is also ideally suited to study molecules of astrochemical interest – both in the laboratory and by using ground-based radioastronomy observatories, and we are just starting to establish this as a new research branch in our group.”
When and why did you start studying rotational spectroscopy of PAHs?
Melanie: ”My interest in PAHs dates back to my PhD research in the group of Jens-Uwe Grabow
at the University of Hannover. During my PhD research, I developed an improved setup for precisely measuring the Stark effect of polar molecules and thus determining their dipole moments
using cavity-based Fourier transform microwave spectroscopy. In 2003, Frank Lovas from the
National Institute of Standards and Technology in Gaithersburg (USA) asked us if we could
measure the Stark effect of corannulene, C20 H10 . In Gaithersburg, he already studied its ro-
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AstroPAH - April 2015 | Issue 17
tational spectrum. C20 H10 can be understood to be the cap of fullerene C60 , saturated with
hydrogen atoms, as shown in Figure 1. From a rotational spectroscopists point of view, it is
an amazingly beautiful symmetric top with C5v symmetry. I was fascinated by the fact that a
molecule consisting purely from carbon and hydrogen can have a dipole moment of more than
2 D.”
Figure 1 - Structure of corannulene. Its dipole moment of 2.07 D was measured in 2005 (Lovas
et al. 2005, J. Am. Chem. Soc 127, 4345-9). We are planning to extend these studies in the
next years.
You recently acquired an ERC grant for your AstroRot project. What does
AstroRot entail?
Melanie: ”In the ERC Starting grant AstroRot we will combine broadband rotational spectroscopy studies in the laboratory with telescope observations, to explore the molecular complexity in interstellar space. We aim at discovering new molecule classes and key chemical
processes. So far, mostly physical reasons were investigated for the observed variations in
molecular abundances. We are interested in studying the influence of chemistry on the molecular composition of the Universe.
One focus will be placed on instrument development for our laboratory spectroscopy studies. Figure 2 shows a photo of our broadband rotational spectrometer that operates in the low
frequency range from 2-8.5 GHz. We are just starting to extend its frequency ranges to have
direct overlap with the new array telescopes (ALMA), i.e., starting in the 70 GHz range. We will
exploit both the cold conditions of a molecular jet and the higher temperatures in a gas cell to
mimic different interstellar conditions. Measurements in the gas cell will allow us to also study
rotational emission of molecules in vibrationally excited states.
The key advantages of chirped-pulse Fourier transform microwave spectroscopy are accurate transition intensities, tremendously reduced measurement times, and unique mixture compatibility. We want to apply this to study PAHs and their complexes (see below).
Furthermore, I am also fascinated by the observation that specific isotopologues, such as
deuterated ammonia ND3 or NHD2 , exhibit increased abundances in interstellar space com5
AstroPAH - April 2015 | Issue 17
pared to what would be expected by their elemental natural abundances. Chemistry is discussed to be the reason for these higher abundances. We want to perform more studies in the
laboratory to further explore this phenomenon.”
Figure 2 - Picture of our broadband rotational spectrometer covering the low frequency range
from 2 to 8.5 GHz.
Which PAHs or related molecules will you be studying for that project?
Melanie: ”We have a long-standing interest in symmetric PAHs such as corannulene, C20 H10 .
In 2005, we were the first to report their rotational spectra and their unexpectedly large dipole
moment of 2.07 D that arises from its curvature. As a consequence, all ten C-H bonds are
roughly pointing into the same direction so that their individual polarizations add up.
We are interested in studying the rotational spectra of corannulene and its complexes with
water and with itself. Furthermore, in the 2005 study, we did not succeed to study its 13 C
isotolopogues in natural abundance. With the broadband rotational spectroscopy approach we
hope to be able to achieve this, which will allow us to precisely determine its molecular structure.
We are also interested in complexes of corannulene with other, smaller polyaromatic hydrocarbons. Since the molecular spectra can be expected to be very rich, broadband rotational
spectroscopy will be the ideal technique to study these systems.”
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AstroPAH - April 2015 | Issue 17
How do you experience work-home balance?
Melanie: ”Work-home or work-life balance in a scientific environment is an ambivalent topic for
me. On the one hand, our working environment is highly flexible. Often, we can plan our daily
schedule rather freely so that it can be combined with the time we need to take care of children,
for example. On the other hand, however, conferences, beamtimes or observatory times let us
travel a lot, which require complicated arrangements. Furthermore, when we as scientists work
on qualifying ourselves for the next stage of academic position, it typically coincides with the
time when we also plan to start a family, which can be very exhausting.”
Do you have any advice for early-career researchers?
Melanie: ”I think it is important to find a research area that fascinates one, to find research
questions that drive one’s curiosity. This will ensure that research remains curiosity-driven
which, to my opinion, is a good way to ensure unexpected new findings and insights.
From a career-planning point of view, I think it would be optimal to change the area of research after the PhD to learn something new during the PostDoc period. These two research
areas can then be naturally combined to form a new, unique research direction.”
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AstroPAH - April 2015 | Issue 17
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Photoluminescence of silicon-vacancy defects in nanodiamonds of different chondrites
A. A. Shiryaev1,2,† , A. V. Fisenko3 , L. F. Semjonova3 , A. A. Khomich4 , I. I.
Vlasov4,5
1
Institute of Physical Chemistry and Electrochemistry RAS, Leninsky pr. 31, korp. 4, 119071, Moscow, Russia
2
Institute of Ore Deposits, Petrography, Geochemistry and Mineralogy RAS, Staromonetny per. 35, 119071,
Moscow, Russia
3
Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Kosygin Street 19, Moscow, Russia
4
General Physics Institute RAS, Vavilov Street 38, 119991 Moscow, Russia
5
National Research Nuclear University MEPhI, Kashirskoe Avenue 31, Moscow 115409, Russia
Photoluminescence spectra show that silicon impurity is present in lattice of some nanodiamond grains (ND) of various chondrites as a silicon-vacancy (SiV) defect. The relative intensity
of the SiV band in the diamond-rich separates depends on chemical composition of meteorites
and on size of ND grains. The strongest signal is found for the size separates enriched in
small grains; thus confirming our earlier conclusion that the SiV defects preferentially reside in
the smallest (≤ 2 nm) grains. The difference in relative intensities of the SiV luminescence in
the diamond-rich separates of individual meteorites are due to variable conditions of thermal
metamorphism of their parent bodies and/or uneven sampling of nanodiamonds populations.
Annealing of separates in air eliminates surface sp2 -carbon, consequently, the SiV luminescence is enhanced. Strong and well-defined luminescence and absorption of the SiV defect is
a promising feature to locate cold (< 250 o C) nanodiamonds in space.
E-mail† : shiryaev@phyche.ac.ru AND a shiryaev@mail.ru
Accepted for publication in Meteoritics and Planetary Science
http://arxiv.org/abs/1502.08031
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Dust dynamics and evolution in expanding HII regions. I.
Radiative drift of neutral and charged grains
V. V. Akimkin1 , M. S. Kirsanova1 , Ya. N. Pavlyuchenkov1 and D. S. Wiebe1
1
Institute of Astronomy of the Russian Academy of Sciences, 48 Pyatnitskaya St. 119017, Moscow, Russia
We consider dust drift under the influence of stellar radiation pressure during the pressuredriven expansion of an HII region using the chemo-dynamical model MARION. Dust size distribution is represented by four dust types: conventional polycyclic aromatic hydrocarbons (PAHs),
very small grains (VSGs), big grains (BGs) and also intermediate-sized grains (ISGs), which are
larger than VSGs and smaller than BGs. The dust is assumed to move at terminal velocity determined locally from the balance between the radiation pressure and gas drag. As Coulomb
drag is an important contribution to the overall gas drag, we evaluate a grain charge evolution
within the HII region for each dust type. BGs are effectively swept out of the HII region. The
spatial distribution of ISGs within the HII region has a double peak structure, with a smaller
inner peak and a higher outer peak. PAHs and VSGs are mostly coupled to the gas. The
mean charge of PAHs is close to zero, so they can become neutral from time to time because
of charge fluctuations. These periods of neutrality occur often enough to cause the removal of
PAHs from the interior of the HII region. For VSGs, the effect of charge fluctuations is less pronounced but still significant. We conclude that accounting for charge dispersion is necessary to
describe the dynamics of small grains.
E-mail: akimkin@inasan.ru
MNRAS 449, 440 (2015)
http://mnras.oxfordjournals.org/content/449/1/440
The electronic spectra of protonated nitrogen-substituted
polycyclic aromatic hydrocarbon molecules
J. A. Noble1 , C. Dedonder1 and C. Jouvet1
1
´ UMR-7345, Physique des Interactions Ioniques et Moleculaires
´
CNRS, Aix-Marseille Universite,
(PIIM): 13397
Marseille Cedex 20, France
Aims This study was designed to examine the viability of protonated nitrogen-substituted polycyclic aromatic hydrocarbons (H+ PANHs) as candidates for the carriers of the diffuse interstellar
bands (DIBs).
Methods We obtained the electronic spectra of two protonated PANH cations, protonated acridine and phenanthridine, using parent ion photo-fragment spectroscopy and generated theoretical electronic spectra using ab initio calculations.
Results We show that the spectra of the two species studied here do not correspond to known
DIBs. However, based on the general properties derived from the spectra of these small protonated nitrogen-substituted PAHs, we propose that larger H+ PANH cations represent good
candidates for DIB carriers due to the expected positions of their electronic transitions in the
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UV-visible and their narrow spectral bands.
E-mail: christophe.jouvet@univ-amu.fr
Accepted for publication in Astronomy & Astrophysics
http://arxiv.org/abs/1503.03329
A Tale of Three Mysterious Spectral Features in CarbonRich Evolved Stars: The 21 µm, 30 µm, and “Unidentified
Infrared” Emission Features
Ajay Mishra1 , Aigen Li1 and B.W. Jiang2
1
Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
2
Department of Astronomy, Beijing Normal University, Beijing 100875, China
The mysterious “21 µm” emission feature seen almost exclusively in the short-lived protoplanetary nebula (PPN) phase of stellar evolution remains unidentified since its discovery two
decades ago. This feature is always accompanied by the equally mysterious, unidentified “30
µm” feature and the so-called “unidentified infrared” (UIR) features at 3.3, 6.2, 7.7, 8.6, and
11.3 µm which are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules.
The 30 µm feature is commonly observed in all stages of stellar evolution from the asymptotic
giant branch (AGB) through PPN to the planetary nebula phase. We explore the interrelations
among the mysterious 21 µm, 30 µm, and UIR features of the 21 µm sources. We derive
the fluxes emitted in the observed UIR, 21 µm, and 30 µm features from published ISO or
Spitzer/IRS spectra. We find that none of these spectral features correlate with each other. This
argues against a common carrier (e.g., thiourea) for both the 21 µm feature and the 30 µm
feature (otherwise these two features should correlate). This also does not support large PAH
clusters as a possible carrier for the 21 µm feature.
E-mail: lia@missouri.edu
Astrophys. J. 802, 39 (2015)
http://adsabs.harvard.edu/abs/2015ApJ...802...39M
PAH Clusters as Sources of Interstellar Infrared Emission
J. E. Roser1,2 and A. Ricca1,2
1
NASA Ames Research Center, Mail Stop 245-6, Building N245, Room 148, P.O. Box 1, Moffett Field, CA 94035,
USA
2
SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043, USA
Polycyclic aromatic hydrocarbons (or PAHs) have been the subject of astrochemical research
for several decades as principal sources of the interstellar aromatic infrared emission bands.
PAH clusters could possibly contribute to these emission bands, but a lack of data on their
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AstroPAH - April 2015 | Issue 17
infrared properties has made this hypothesis difficult to evaluate. Here we investigate homogeneous neutral PAH clusters by measuring the mid-infrared absorption spectra of the five
nonlinear PAH molecules phenanthrene, chrysene, pyrene, perylene, and benzo[ghi]perylene
within solid argon ice at a fixed temperature of 5 K. We attribute observed spectral shifts in their
principal absorption bands as a function of argon/PAH ratio to clustering of the PAH molecules
within the argon matrix. These shifts are related to the cluster structures forming in the matrix
and the topology of the monomer PAH molecule. We predict that interstellar PAH molecules that
are relatively large (no fewer than 50 carbon atoms per molecule) and compact will have clusters that contribute to the asymmetrically red-shaded profile of the interstellar 11.2 µm emission
band.
E-mail: Joseph.E.Roser@nasa.gov
The Astrophysical Journal, 801, 108 (2015)
http://iopscience.iop.org/0004-637X/801/2/108/article
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From interstellar ices to
polycyclic aromatic hydrocarbons:
A symposium to honor Lou Allamandola’s contributions to
the molecular Universe
Annapolis - Maryland - USA
September 13-17, 2015
**Deadline for abstract submission: 26 June 2015**
This is the first announcement of the meeting ”From interstellar ices to polycyclic aromatic
hydrocarbons: A symposium to honor Lou Allamandola’s contributions to the molecular Universe”. Abstracts should be submitted by June 26 for consideration. Details on the meeting and
registration will be available on the website in the near future:
http://ices2pahs.strw.leidenuniv.nl/index.html
Extensive advances in the field of Astrochemistry have been made thanks to simultaneous
efforts in astronomical infrared spectroscopy and to dedicated laboratory simulations and theoretical studies aimed at reproducing observed spectra throughout the interstellar medium. The
molecular complexity, both organic and mineral, found in inter/proto-stellar and solar system
environments have been attributed to primarily grain-surface and bulk chemistry reactions.
This symposium will be comprised of contributions from participants working on dedicated
laboratory experiments, theoretical calculations of basic processes and chemical reaction networks, as well as astronomical observations of complex molecules and, more generally solid
state materials in space. This gathering is in honor of a major influence to this area of Astrochemistry, Dr. Louis Allamandola, one of the leading spokespersons of the interstellar polycyclic
aromatic hydrocarbon (PAH) model.
The scientific topics of this meeting include:
• Ices - Spectroscopy, Energetic Processing
• Surface Chemistry
• PAHs in Ices
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• Identification, Observation, and models of PAHs
• Formation of complex species in Ices - Astrobiology
The format of the meeting will consist of invited talks, contributed talks, and posters. A list of
invited speakers will be available on the website soon.
The Symposium will be held at the Historic Inns of Annapolis located in Annapolis, MD USA
(http://www.historicinnsofannapolis.com/).
We are looking forward to an exciting meeting and hope to welcome you in Annapolis this
fall.
The Scientific Organizing Committee:
Stefanie Milam (NASA/GSFC)
Alexander Tielens (Univ. Leiden)
Jason Dworkin (NASA/GSFC)
Doug Hudgins (NASA/HQ)
Jamie Elsila (NASA/GSFC)
Murthy Gudipati (NASA/JPL)
Max Bernstein (NASA/HQ)
Louis d’Hendecourt (Universite´ Paris-Sud)
International Symposium on
Polynuclear Aromatic Hydrocarbons
‘Cite´ Mondiale Convention Centre’ in Bordeaux , France
September 13-17, 2015
http://ispac2015.ism.u-bordeaux1.fr/?lang=en
ISPAC 2015 will focus on the research of Polycyclic Aromatic Compounds (PACs) on multiple
fronts of analytical measurements, toxicology, organic synthesis, human exposure and health
effects, and environmental presences, sources, fate and transport.
It is a forum that brings together researchers worldwide to communicate, learn and advance
the field of PAC. In addition, we intend to have an exhibition involving chemical products, analytical instrumentations and services involving PACs.
We will welcome proposals for short courses, arranged sessions and vendors’ seminars.
Several best presentation awards will be distributed to young researchers. Finally the ISPAC
2015 Award will be given to a prominent research scientist in the field of PACs.
ORGANISERS: ISM / CNRS
EMAILS FOR CONTACT: ispac2015@u-bordeaux.fr
k.ndiaye@ism.u-bordeaux1.fr
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NEW JOURNAL:
Molecular Astrophysics
The journal is welcoming submissions!
http://www.elsevier.com/locate/molap
Molecular Astrophysics aims to provide a platform for scientists studying the chemical processes that form and deconstruct molecules, and control chemical abundances in the universe,
particularly on Solar System objects such as planets, moons, and comets, in the atmospheres
of exoplanets, as well as in regions of star and planet formation in the Interstellar Medium of
galaxies.
This journal is subscription based with the option to publish Open Access.
First issue expected in fall 2015 and freely available online for the first year!
Editor-in-Chief
Alexander Tielens, Leiden University, the Netherlands
Handling Editors
Francois Dulieu, Universit/’e de Cergy-Pontoise, France
Wolf Geppert, Stockholm University, Sweden
Kevin Heng, University of Bern, Switzerland
Christine Joblin, Universit/’e de Toulouse, France
Timothy Lee, NASA Ames Research Center, USA
Peter Sarre, University of Nottingham, UK
Satoshi Yamamoto, University of Tokyo, Japan
Editorial Board Members
Louis Allamandola, NASA Ames Research Center, USA
Peter Bernath, Old Dominion University, USA
Anil Bhardwaj, Vikram Sarabhai Space Centre, India
Pepe Cernicharo, CSIC Centro de Astrobiologia, Spain
Eric Herbst, University of Virginia, USA
Nigel Mason, Open University, United Kingdom
Michael J. Mumma, NASA Goddard Space Flight Center, USA
Sun Kwok, The University of Hong Kong, China
Heike Rauer, Deutsches Zentrum fur Luft und Raumfahrt (DLR), Germany
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AstroPAH Newsletter
http://astropah-news.strw.leidenuniv.nl
astropah@strw.leidenuniv.nl
Next issue: 19 May 2015
Submission deadline: 8 May 2015
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